Field of the Invention
Embodiments of the present invention relate to the technology field of a lighting device.
Description of the Related Arts
An LED (Light Emitted Diode) device is a device which converts an electrical signal to infrared rays or light using a composition semiconductor property. Unlike a florescent lamp, since the LED device does not use harmful substances such as mercury and the like, it is advantageous that the LED device has a low possibility to cause environmental pollution and a long life span compared to a conventional light source. Also, it is advantageous that the LED device spends low electricity compared to the conventional light source and has excellent visibility and low brilliantness due to a high color temperature.
Accordingly, a current lighting device has been developed from a structure, in which a traditional light source such as a conventional incandescent lamp or a florescent lamp is used, to a structure, in which the aforesaid LED device is used as a light source. In particular, by using a light guide plate as disclosed in Korean Laid-Open Patent Publication No. 10-2012-0009209, the lighting device which performs a surface light-emitting function has been provided.
The aforesaid lighting device is composed in a structure in which a flat light guide plate is disposed on a substrate, and a plurality of side view type LEDs is disposed on a side of the light guide plate in an array shape. Here, the light guide plate is a kind of plastic molding lens which functions to uniformly supply light emitted from the LEDs. Accordingly, in the conventional lighting device, the light guide plate is used as an essential component. However, due to a thickness of the light guide plate itself, there is a limitation to make the thickness of an entire product thin. Furthermore, as a material of the light guide plate is not flexible, it is disadvantageous that it would be difficult to apply the light guide plate to a part in which a bend is formed, and thus a product plan and design cannot be easily changed.
Also, as the light is partially emitted to the side of the light guide plate, light loss is generated. Thus, it is problematic that the efficiency of light is reduced. Furthermore, as a temperature of the LEDs increases at the time of light emission, it is also problematic that the LEDs' characteristics (e.g. luminous intensity and wavelength transition) are changed.
Also, in the case of the existing lighting device composed of a surface light source, since a haze of more than 50% is used by a diffusion plate, it is disadvantageous that the efficiency of light is low and a thickness increases.